This project is divided into two groups. Both groups were inoculated with HIV-2/KR, a non-pathogenic molecular clone group 1 on 6/14/94 and group 2 on 8/30/94. Group 1 was challenged twice with HIV-2/287, a highly pathogenic isolate derived from in vivo passage in Macaca nemestrina. The first challenge dose, 10 TCID (8/18/95), produced only limited infection. The second challenge dose, 1000 TCID (6/17/96), infected the nave macaques, but produced little to no infection in the macaques previously exposed. The single exception, macaque L93210, was depleted of CD4+ cells by 10 weeks post-inoculation. One macaque died of acute gastric dilatation; one was euthanatized due to deterioration in a femoral joint that compromised use of the leg. Neither death appeared related to the experimental interventions. The second group of macaques was challenged with 100 TCID (10/8/96). Although all the macaques were infected, three of the seven macaques previously exposed to the KR clone did not develop depletion of the CD4+ cells up to 64 weeks post-challenge. This project is now closed and the macaques will be necropsied for histological examination.